Notes

All arithmetic is performed modulo 2^n, where n is the number of
bits in the type. One non-obvious consequence of this is that negate
should not raise an error on negative arguments.

For coercing between any two integer types, use
fromIntegral, which is specialized for all the
common cases so should be fast enough. Coercing word types to and
from integer types preserves representation, not sign.

The rules that hold for Enum instances over a bounded type
such as Int (see the section of the Haskell report dealing
with arithmetic sequences) also hold for the Enum instances
over the various Word types defined here.

Right and left shifts by amounts greater than or equal to the width
of the type result in a zero result. This is contrary to the
behaviour in C, which is undefined; a common interpretation is to
truncate the shift count to the width of the type, for example 1 <<
32 == 1 in some C implementations.